// Copyright 2017-2019 by Martin Moene
//
// string-view lite, a C++17-like string_view for C++98 and later.
// For more information see https://github.com/martinmoene/string-view-lite
//
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)

#pragma once

#ifndef NONSTD_SV_LITE_H_INCLUDED
#define NONSTD_SV_LITE_H_INCLUDED

#define string_view_lite_MAJOR 1
#define string_view_lite_MINOR 4
#define string_view_lite_PATCH 0

#define string_view_lite_VERSION                             \
  nssv_STRINGIFY(string_view_lite_MAJOR) "." nssv_STRINGIFY( \
      string_view_lite_MINOR) "." nssv_STRINGIFY(string_view_lite_PATCH)

#define nssv_STRINGIFY(x) nssv_STRINGIFY_(x)
#define nssv_STRINGIFY_(x) #x

// string-view lite configuration:

#define nssv_STRING_VIEW_DEFAULT 0
#define nssv_STRING_VIEW_NONSTD 1
#define nssv_STRING_VIEW_STD 2

#if !defined(nssv_CONFIG_SELECT_STRING_VIEW)
#define nssv_CONFIG_SELECT_STRING_VIEW \
  (nssv_HAVE_STD_STRING_VIEW ? nssv_STRING_VIEW_STD : nssv_STRING_VIEW_NONSTD)
#endif

#if defined(nssv_CONFIG_SELECT_STD_STRING_VIEW) || \
    defined(nssv_CONFIG_SELECT_NONSTD_STRING_VIEW)
#error nssv_CONFIG_SELECT_STD_STRING_VIEW and nssv_CONFIG_SELECT_NONSTD_STRING_VIEW are deprecated and removed, please use nssv_CONFIG_SELECT_STRING_VIEW=nssv_STRING_VIEW_...
#endif

#ifndef nssv_CONFIG_STD_SV_OPERATOR
#define nssv_CONFIG_STD_SV_OPERATOR 0
#endif

#ifndef nssv_CONFIG_USR_SV_OPERATOR
#define nssv_CONFIG_USR_SV_OPERATOR 1
#endif

#ifdef nssv_CONFIG_CONVERSION_STD_STRING
#define nssv_CONFIG_CONVERSION_STD_STRING_CLASS_METHODS \
  nssv_CONFIG_CONVERSION_STD_STRING
#define nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS \
  nssv_CONFIG_CONVERSION_STD_STRING
#endif

#ifndef nssv_CONFIG_CONVERSION_STD_STRING_CLASS_METHODS
#define nssv_CONFIG_CONVERSION_STD_STRING_CLASS_METHODS 1
#endif

#ifndef nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS
#define nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS 1
#endif

// Control presence of exception handling (try and auto discover):

#ifndef nssv_CONFIG_NO_EXCEPTIONS
#if defined(__cpp_exceptions) || defined(__EXCEPTIONS) || defined(_CPPUNWIND)
#define nssv_CONFIG_NO_EXCEPTIONS 0
#else
#define nssv_CONFIG_NO_EXCEPTIONS 1
#endif
#endif

// C++ language version detection (C++20 is speculative):
// Note: VC14.0/1900 (VS2015) lacks too much from C++14.

#ifndef nssv_CPLUSPLUS
#if defined(_MSVC_LANG) && !defined(__clang__)
#define nssv_CPLUSPLUS (_MSC_VER == 1900 ? 201103L : _MSVC_LANG)
#else
#define nssv_CPLUSPLUS __cplusplus
#endif
#endif

#define nssv_CPP98_OR_GREATER (nssv_CPLUSPLUS >= 199711L)
#define nssv_CPP11_OR_GREATER (nssv_CPLUSPLUS >= 201103L)
#define nssv_CPP11_OR_GREATER_ (nssv_CPLUSPLUS >= 201103L)
#define nssv_CPP14_OR_GREATER (nssv_CPLUSPLUS >= 201402L)
#define nssv_CPP17_OR_GREATER (nssv_CPLUSPLUS >= 201703L)
#define nssv_CPP20_OR_GREATER (nssv_CPLUSPLUS >= 202000L)

// use C++17 std::string_view if available and requested:

#if nssv_CPP17_OR_GREATER && defined(__has_include)
#if __has_include(<string_view> )
#define nssv_HAVE_STD_STRING_VIEW 1
#else
#define nssv_HAVE_STD_STRING_VIEW 0
#endif
#else
#define nssv_HAVE_STD_STRING_VIEW 0
#endif

#define nssv_USES_STD_STRING_VIEW                                   \
  ((nssv_CONFIG_SELECT_STRING_VIEW == nssv_STRING_VIEW_STD) ||      \
   ((nssv_CONFIG_SELECT_STRING_VIEW == nssv_STRING_VIEW_DEFAULT) && \
    nssv_HAVE_STD_STRING_VIEW))

#define nssv_HAVE_STARTS_WITH \
  (nssv_CPP20_OR_GREATER || !nssv_USES_STD_STRING_VIEW)
#define nssv_HAVE_ENDS_WITH nssv_HAVE_STARTS_WITH

//
// Use C++17 std::string_view:
//

#if nssv_USES_STD_STRING_VIEW

#include <string_view>

// Extensions for std::string:

#if nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS

namespace nonstd {

template <class CharT, class Traits, class Allocator = std::allocator<CharT> >
std::basic_string<CharT, Traits, Allocator> to_string(
    std::basic_string_view<CharT, Traits> v, Allocator const& a = Allocator()) {
  return std::basic_string<CharT, Traits, Allocator>(v.begin(), v.end(), a);
}

template <class CharT, class Traits, class Allocator>
std::basic_string_view<CharT, Traits> to_string_view(
    std::basic_string<CharT, Traits, Allocator> const& s) {
  return std::basic_string_view<CharT, Traits>(s.data(), s.size());
}

// Literal operators sv and _sv:

#if nssv_CONFIG_STD_SV_OPERATOR

using namespace std::literals::string_view_literals;

#endif

#if nssv_CONFIG_USR_SV_OPERATOR

inline namespace literals {
inline namespace string_view_literals {
constexpr std::string_view operator"" _sv(const char* str,
                                          size_t len) noexcept  // (1)
{
  return std::string_view{str, len};
}

constexpr std::u16string_view operator"" _sv(const char16_t* str,
                                             size_t len) noexcept  // (2)
{
  return std::u16string_view{str, len};
}

constexpr std::u32string_view operator"" _sv(const char32_t* str,
                                             size_t len) noexcept  // (3)
{
  return std::u32string_view{str, len};
}

constexpr std::wstring_view operator"" _sv(const wchar_t* str,
                                           size_t len) noexcept  // (4)
{
  return std::wstring_view{str, len};
}

}  // namespace string_view_literals
}  // namespace literals

#endif  // nssv_CONFIG_USR_SV_OPERATOR

}  // namespace nonstd

#endif  // nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS

namespace nonstd {

using std::basic_string_view;
using std::string_view;
using std::u16string_view;
using std::u32string_view;
using std::wstring_view;

// literal "sv" and "_sv", see above

using std::operator==;
using std::operator!=;
using std::operator<;
using std::operator<=;
using std::operator>;
using std::operator>=;

using std::operator<<;

}  // namespace nonstd

#else  // nssv_HAVE_STD_STRING_VIEW

//
// Before C++17: use string_view lite:
//

// Compiler versions:
//
// MSVC++ 6.0  _MSC_VER == 1200 (Visual Studio 6.0)
// MSVC++ 7.0  _MSC_VER == 1300 (Visual Studio .NET 2002)
// MSVC++ 7.1  _MSC_VER == 1310 (Visual Studio .NET 2003)
// MSVC++ 8.0  _MSC_VER == 1400 (Visual Studio 2005)
// MSVC++ 9.0  _MSC_VER == 1500 (Visual Studio 2008)
// MSVC++ 10.0 _MSC_VER == 1600 (Visual Studio 2010)
// MSVC++ 11.0 _MSC_VER == 1700 (Visual Studio 2012)
// MSVC++ 12.0 _MSC_VER == 1800 (Visual Studio 2013)
// MSVC++ 14.0 _MSC_VER == 1900 (Visual Studio 2015)
// MSVC++ 14.1 _MSC_VER >= 1910 (Visual Studio 2017)

#if defined(_MSC_VER) && !defined(__clang__)
#define nssv_COMPILER_MSVC_VER (_MSC_VER)
#define nssv_COMPILER_MSVC_VERSION \
  (_MSC_VER / 10 - 10 * (5 + (_MSC_VER < 1900)))
#else
#define nssv_COMPILER_MSVC_VER 0
#define nssv_COMPILER_MSVC_VERSION 0
#endif

#define nssv_COMPILER_VERSION(major, minor, patch) \
  (10 * (10 * (major) + (minor)) + (patch))

#if defined(__clang__)
#define nssv_COMPILER_CLANG_VERSION \
  nssv_COMPILER_VERSION(__clang_major__, __clang_minor__, __clang_patchlevel__)
#else
#define nssv_COMPILER_CLANG_VERSION 0
#endif

#if defined(__GNUC__) && !defined(__clang__)
#define nssv_COMPILER_GNUC_VERSION \
  nssv_COMPILER_VERSION(__GNUC__, __GNUC_MINOR__, __GNUC_PATCHLEVEL__)
#else
#define nssv_COMPILER_GNUC_VERSION 0
#endif

// half-open range [lo..hi):
#define nssv_BETWEEN(v, lo, hi) ((lo) <= (v) && (v) < (hi))

// Presence of language and library features:

#ifdef _HAS_CPP0X
#define nssv_HAS_CPP0X _HAS_CPP0X
#else
#define nssv_HAS_CPP0X 0
#endif

// Unless defined otherwise below, consider VC14 as C++11 for variant-lite:

#if nssv_COMPILER_MSVC_VER >= 1900
#undef nssv_CPP11_OR_GREATER
#define nssv_CPP11_OR_GREATER 1
#endif

#define nssv_CPP11_90 (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1500)
#define nssv_CPP11_100 \
  (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1600)
#define nssv_CPP11_110 \
  (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1700)
#define nssv_CPP11_120 \
  (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1800)
#define nssv_CPP11_140 \
  (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1900)
#define nssv_CPP11_141 \
  (nssv_CPP11_OR_GREATER_ || nssv_COMPILER_MSVC_VER >= 1910)

#define nssv_CPP14_000 (nssv_CPP14_OR_GREATER)
#define nssv_CPP17_000 (nssv_CPP17_OR_GREATER)

// Presence of C++11 language features:

#define nssv_HAVE_CONSTEXPR_11 nssv_CPP11_140
#define nssv_HAVE_EXPLICIT_CONVERSION nssv_CPP11_140
#define nssv_HAVE_INLINE_NAMESPACE nssv_CPP11_140
#define nssv_HAVE_NOEXCEPT nssv_CPP11_140
#define nssv_HAVE_NULLPTR nssv_CPP11_100
#define nssv_HAVE_REF_QUALIFIER nssv_CPP11_140
#define nssv_HAVE_UNICODE_LITERALS nssv_CPP11_140
#define nssv_HAVE_USER_DEFINED_LITERALS nssv_CPP11_140
#define nssv_HAVE_WCHAR16_T nssv_CPP11_100
#define nssv_HAVE_WCHAR32_T nssv_CPP11_100

#if !((nssv_CPP11_OR_GREATER && nssv_COMPILER_CLANG_VERSION) || \
      nssv_BETWEEN(nssv_COMPILER_CLANG_VERSION, 300, 400))
#define nssv_HAVE_STD_DEFINED_LITERALS nssv_CPP11_140
#else
#define nssv_HAVE_STD_DEFINED_LITERALS 0
#endif

// Presence of C++14 language features:

#define nssv_HAVE_CONSTEXPR_14 nssv_CPP14_000

// Presence of C++17 language features:

#define nssv_HAVE_NODISCARD nssv_CPP17_000

// Presence of C++ library features:

#define nssv_HAVE_STD_HASH nssv_CPP11_120

// C++ feature usage:

#if nssv_HAVE_CONSTEXPR_11
#define nssv_constexpr constexpr
#else
#define nssv_constexpr /*constexpr*/
#endif

#if nssv_HAVE_CONSTEXPR_14
#define nssv_constexpr14 constexpr
#else
#define nssv_constexpr14 /*constexpr*/
#endif

#if nssv_HAVE_EXPLICIT_CONVERSION
#define nssv_explicit explicit
#else
#define nssv_explicit /*explicit*/
#endif

#if nssv_HAVE_INLINE_NAMESPACE
#define nssv_inline_ns inline
#else
#define nssv_inline_ns /*inline*/
#endif

#if nssv_HAVE_NOEXCEPT
#define nssv_noexcept noexcept
#else
#define nssv_noexcept /*noexcept*/
#endif

//#if nssv_HAVE_REF_QUALIFIER
//# define nssv_ref_qual  &
//# define nssv_refref_qual  &&
//#else
//# define nssv_ref_qual  /*&*/
//# define nssv_refref_qual  /*&&*/
//#endif

#if nssv_HAVE_NULLPTR
#define nssv_nullptr nullptr
#else
#define nssv_nullptr NULL
#endif

#if nssv_HAVE_NODISCARD
#define nssv_nodiscard [[nodiscard]]
#else
#define nssv_nodiscard /*[[nodiscard]]*/
#endif

// Additional includes:

#include <algorithm>
#include <cassert>
#include <iterator>
#include <limits>
#include <ostream>
#include <string>  // std::char_traits<>

#if !nssv_CONFIG_NO_EXCEPTIONS
#include <stdexcept>
#endif

#if nssv_CPP11_OR_GREATER
#include <type_traits>
#endif

// Clang, GNUC, MSVC warning suppression macros:

#if defined(__clang__)
#pragma clang diagnostic ignored "-Wreserved-user-defined-literal"
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wuser-defined-literals"
#elif defined(__GNUC__)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wliteral-suffix"
#endif  // __clang__

#if nssv_COMPILER_MSVC_VERSION >= 140
#define nssv_SUPPRESS_MSGSL_WARNING(expr) [[gsl::suppress(expr)]]
#define nssv_SUPPRESS_MSVC_WARNING(code, descr) \
  __pragma(warning(suppress : code))
#define nssv_DISABLE_MSVC_WARNINGS(codes) \
  __pragma(warning(push)) __pragma(warning(disable : codes))
#else
#define nssv_SUPPRESS_MSGSL_WARNING(expr)
#define nssv_SUPPRESS_MSVC_WARNING(code, descr)
#define nssv_DISABLE_MSVC_WARNINGS(codes)
#endif

#if defined(__clang__)
#define nssv_RESTORE_WARNINGS() _Pragma("clang diagnostic pop")
#elif defined(__GNUC__)
#define nssv_RESTORE_WARNINGS() _Pragma("GCC diagnostic pop")
#elif nssv_COMPILER_MSVC_VERSION >= 140
#define nssv_RESTORE_WARNINGS() __pragma(warning(pop))
#else
#define nssv_RESTORE_WARNINGS()
#endif

// Suppress the following MSVC (GSL) warnings:
// - C4455, non-gsl   : 'operator ""sv': literal suffix identifiers that do not
//                      start with an underscore are reserved
// - C26472, gsl::t.1 : don't use a static_cast for arithmetic conversions;
//                      use brace initialization, gsl::narrow_cast or gsl::narow
// - C26481: gsl::b.1 : don't use pointer arithmetic. Use span instead

nssv_DISABLE_MSVC_WARNINGS(4455 26481 26472)
    // nssv_DISABLE_CLANG_WARNINGS( "-Wuser-defined-literals" )
    // nssv_DISABLE_GNUC_WARNINGS( -Wliteral-suffix )

    namespace nonstd {
  namespace sv_lite {

#if nssv_CPP11_OR_GREATER

  namespace detail {

  // Expect tail call optimization to make length() non-recursive:

  template <typename CharT>
  inline constexpr std::size_t length(CharT* s, std::size_t result = 0) {
    return *s == '\0' ? result : length(s + 1, result + 1);
  }

  }  // namespace detail

#endif  // nssv_CPP11_OR_GREATER

  template <class CharT, class Traits = std::char_traits<CharT> >
  class basic_string_view;

  //
  // basic_string_view:
  //

  template <class CharT, class Traits /* = std::char_traits<CharT> */
            >
  class basic_string_view {
   public:
    // Member types:

    typedef Traits traits_type;
    typedef CharT value_type;

    typedef CharT* pointer;
    typedef CharT const* const_pointer;
    typedef CharT& reference;
    typedef CharT const& const_reference;

    typedef const_pointer iterator;
    typedef const_pointer const_iterator;
    typedef std::reverse_iterator<const_iterator> reverse_iterator;
    typedef std::reverse_iterator<const_iterator> const_reverse_iterator;

    typedef std::size_t size_type;
    typedef std::ptrdiff_t difference_type;

    // 24.4.2.1 Construction and assignment:

    nssv_constexpr basic_string_view() nssv_noexcept : data_(nssv_nullptr),
                                                       size_(0) {}

#if nssv_CPP11_OR_GREATER
    nssv_constexpr basic_string_view(basic_string_view const& other)
        nssv_noexcept = default;
#else
    nssv_constexpr basic_string_view(basic_string_view const& other)
        nssv_noexcept : data_(other.data_),
                        size_(other.size_) {}
#endif

    nssv_constexpr basic_string_view(CharT const* s, size_type count)
        nssv_noexcept  // non-standard noexcept
        : data_(s),
          size_(count) {}

    nssv_constexpr basic_string_view(CharT const* s)
        nssv_noexcept  // non-standard noexcept
        : data_(s)
#if nssv_CPP17_OR_GREATER
        ,
          size_(Traits::length(s))
#elif nssv_CPP11_OR_GREATER
        ,
          size_(detail::length(s))
#else
        ,
          size_(Traits::length(s))
#endif
    {
    }

    // Assignment:

#if nssv_CPP11_OR_GREATER
    nssv_constexpr14 basic_string_view& operator=(
        basic_string_view const& other) nssv_noexcept = default;
#else
    nssv_constexpr14 basic_string_view& operator=(
        basic_string_view const& other) nssv_noexcept {
      data_ = other.data_;
      size_ = other.size_;
      return *this;
    }
#endif

    // 24.4.2.2 Iterator support:

    nssv_constexpr const_iterator begin() const nssv_noexcept { return data_; }
    nssv_constexpr const_iterator end() const nssv_noexcept {
      return data_ + size_;
    }

    nssv_constexpr const_iterator cbegin() const nssv_noexcept {
      return begin();
    }
    nssv_constexpr const_iterator cend() const nssv_noexcept { return end(); }

    nssv_constexpr const_reverse_iterator rbegin() const nssv_noexcept {
      return const_reverse_iterator(end());
    }
    nssv_constexpr const_reverse_iterator rend() const nssv_noexcept {
      return const_reverse_iterator(begin());
    }

    nssv_constexpr const_reverse_iterator crbegin() const nssv_noexcept {
      return rbegin();
    }
    nssv_constexpr const_reverse_iterator crend() const nssv_noexcept {
      return rend();
    }

    // 24.4.2.3 Capacity:

    nssv_constexpr size_type size() const nssv_noexcept { return size_; }
    nssv_constexpr size_type length() const nssv_noexcept { return size_; }
    nssv_constexpr size_type max_size() const nssv_noexcept {
      return (std::numeric_limits<size_type>::max)();
    }

    // since C++20
    nssv_nodiscard nssv_constexpr bool empty() const nssv_noexcept {
      return 0 == size_;
    }

    // 24.4.2.4 Element access:

    nssv_constexpr const_reference operator[](size_type pos) const {
      return data_at(pos);
    }

    nssv_constexpr14 const_reference at(size_type pos) const {
#if nssv_CONFIG_NO_EXCEPTIONS
      assert(pos < size());
#else
      if (pos >= size()) {
        throw std::out_of_range("nonstd::string_view::at()");
      }
#endif
      return data_at(pos);
    }

    nssv_constexpr const_reference front() const { return data_at(0); }
    nssv_constexpr const_reference back() const { return data_at(size() - 1); }

    nssv_constexpr const_pointer data() const nssv_noexcept { return data_; }

    // 24.4.2.5 Modifiers:

    nssv_constexpr14 void remove_prefix(size_type n) {
      assert(n <= size());
      data_ += n;
      size_ -= n;
    }

    nssv_constexpr14 void remove_suffix(size_type n) {
      assert(n <= size());
      size_ -= n;
    }

    nssv_constexpr14 void swap(basic_string_view& other) nssv_noexcept {
      using std::swap;
      swap(data_, other.data_);
      swap(size_, other.size_);
    }

    // 24.4.2.6 String operations:

    size_type copy(CharT* dest, size_type n, size_type pos = 0) const {
#if nssv_CONFIG_NO_EXCEPTIONS
      assert(pos <= size());
#else
      if (pos > size()) {
        throw std::out_of_range("nonstd::string_view::copy()");
      }
#endif
      const size_type rlen = (std::min)(n, size() - pos);

      (void)Traits::copy(dest, data() + pos, rlen);

      return rlen;
    }

    nssv_constexpr14 basic_string_view substr(size_type pos = 0,
                                              size_type n = npos) const {
#if nssv_CONFIG_NO_EXCEPTIONS
      assert(pos <= size());
#else
      if (pos > size()) {
        throw std::out_of_range("nonstd::string_view::substr()");
      }
#endif
      return basic_string_view(data() + pos, (std::min)(n, size() - pos));
    }

    // compare(), 6x:

    nssv_constexpr14 int compare(basic_string_view other) const
        nssv_noexcept  // (1)
    {
      if (const int result = Traits::compare(
              data(), other.data(), (std::min)(size(), other.size()))) {
        return result;
      }

      return size() == other.size() ? 0 : size() < other.size() ? -1 : 1;
    }

    nssv_constexpr int compare(size_type pos1, size_type n1,
                               basic_string_view other) const  // (2)
    {
      return substr(pos1, n1).compare(other);
    }

    nssv_constexpr int compare(size_type pos1, size_type n1,
                               basic_string_view other, size_type pos2,
                               size_type n2) const  // (3)
    {
      return substr(pos1, n1).compare(other.substr(pos2, n2));
    }

    nssv_constexpr int compare(CharT const* s) const  // (4)
    {
      return compare(basic_string_view(s));
    }

    nssv_constexpr int compare(size_type pos1, size_type n1,
                               CharT const* s) const  // (5)
    {
      return substr(pos1, n1).compare(basic_string_view(s));
    }

    nssv_constexpr int compare(size_type pos1, size_type n1, CharT const* s,
                               size_type n2) const  // (6)
    {
      return substr(pos1, n1).compare(basic_string_view(s, n2));
    }

    // 24.4.2.7 Searching:

    // starts_with(), 3x, since C++20:

    nssv_constexpr bool starts_with(basic_string_view v) const
        nssv_noexcept  // (1)
    {
      return size() >= v.size() && compare(0, v.size(), v) == 0;
    }

    nssv_constexpr bool starts_with(CharT c) const nssv_noexcept  // (2)
    {
      return starts_with(basic_string_view(&c, 1));
    }

    nssv_constexpr bool starts_with(CharT const* s) const  // (3)
    {
      return starts_with(basic_string_view(s));
    }

    // ends_with(), 3x, since C++20:

    nssv_constexpr bool ends_with(basic_string_view v) const
        nssv_noexcept  // (1)
    {
      return size() >= v.size() && compare(size() - v.size(), npos, v) == 0;
    }

    nssv_constexpr bool ends_with(CharT c) const nssv_noexcept  // (2)
    {
      return ends_with(basic_string_view(&c, 1));
    }

    nssv_constexpr bool ends_with(CharT const* s) const  // (3)
    {
      return ends_with(basic_string_view(s));
    }

    // find(), 4x:

    nssv_constexpr14 size_type
    find(basic_string_view v, size_type pos = 0) const nssv_noexcept  // (1)
    {
      return assert(v.size() == 0 || v.data() != nssv_nullptr),
             pos >= size()
                 ? npos
                 : to_pos(std::search(cbegin() + pos, cend(), v.cbegin(),
                                      v.cend(), Traits::eq));
    }

    nssv_constexpr14 size_type
    find(CharT c, size_type pos = 0) const nssv_noexcept  // (2)
    {
      return find(basic_string_view(&c, 1), pos);
    }

    nssv_constexpr14 size_type find(CharT const* s, size_type pos,
                                    size_type n) const  // (3)
    {
      return find(basic_string_view(s, n), pos);
    }

    nssv_constexpr14 size_type find(CharT const* s,
                                    size_type pos = 0) const  // (4)
    {
      return find(basic_string_view(s), pos);
    }

    // rfind(), 4x:

    nssv_constexpr14 size_type
    rfind(basic_string_view v, size_type pos = npos) const nssv_noexcept  // (1)
    {
      if (size() < v.size()) {
        return npos;
      }

      if (v.empty()) {
        return (std::min)(size(), pos);
      }

      const_iterator last =
          cbegin() + (std::min)(size() - v.size(), pos) + v.size();
      const_iterator result =
          std::find_end(cbegin(), last, v.cbegin(), v.cend(), Traits::eq);

      return result != last ? size_type(result - cbegin()) : npos;
    }

    nssv_constexpr14 size_type
    rfind(CharT c, size_type pos = npos) const nssv_noexcept  // (2)
    {
      return rfind(basic_string_view(&c, 1), pos);
    }

    nssv_constexpr14 size_type rfind(CharT const* s, size_type pos,
                                     size_type n) const  // (3)
    {
      return rfind(basic_string_view(s, n), pos);
    }

    nssv_constexpr14 size_type rfind(CharT const* s,
                                     size_type pos = npos) const  // (4)
    {
      return rfind(basic_string_view(s), pos);
    }

    // find_first_of(), 4x:

    nssv_constexpr size_type find_first_of(
        basic_string_view v, size_type pos = 0) const nssv_noexcept  // (1)
    {
      return pos >= size()
                 ? npos
                 : to_pos(std::find_first_of(cbegin() + pos, cend(), v.cbegin(),
                                             v.cend(), Traits::eq));
    }

    nssv_constexpr size_type
    find_first_of(CharT c, size_type pos = 0) const nssv_noexcept  // (2)
    {
      return find_first_of(basic_string_view(&c, 1), pos);
    }

    nssv_constexpr size_type find_first_of(CharT const* s, size_type pos,
                                           size_type n) const  // (3)
    {
      return find_first_of(basic_string_view(s, n), pos);
    }

    nssv_constexpr size_type find_first_of(CharT const* s,
                                           size_type pos = 0) const  // (4)
    {
      return find_first_of(basic_string_view(s), pos);
    }

    // find_last_of(), 4x:

    nssv_constexpr size_type find_last_of(
        basic_string_view v, size_type pos = npos) const nssv_noexcept  // (1)
    {
      return empty() ? npos
                     : pos >= size()
                           ? find_last_of(v, size() - 1)
                           : to_pos(std::find_first_of(
                                 const_reverse_iterator(cbegin() + pos + 1),
                                 crend(), v.cbegin(), v.cend(), Traits::eq));
    }

    nssv_constexpr size_type
    find_last_of(CharT c, size_type pos = npos) const nssv_noexcept  // (2)
    {
      return find_last_of(basic_string_view(&c, 1), pos);
    }

    nssv_constexpr size_type find_last_of(CharT const* s, size_type pos,
                                          size_type count) const  // (3)
    {
      return find_last_of(basic_string_view(s, count), pos);
    }

    nssv_constexpr size_type find_last_of(CharT const* s,
                                          size_type pos = npos) const  // (4)
    {
      return find_last_of(basic_string_view(s), pos);
    }

    // find_first_not_of(), 4x:

    nssv_constexpr size_type find_first_not_of(
        basic_string_view v, size_type pos = 0) const nssv_noexcept  // (1)
    {
      return pos >= size()
                 ? npos
                 : to_pos(std::find_if(cbegin() + pos, cend(), not_in_view(v)));
    }

    nssv_constexpr size_type
    find_first_not_of(CharT c, size_type pos = 0) const nssv_noexcept  // (2)
    {
      return find_first_not_of(basic_string_view(&c, 1), pos);
    }

    nssv_constexpr size_type find_first_not_of(CharT const* s, size_type pos,
                                               size_type count) const  // (3)
    {
      return find_first_not_of(basic_string_view(s, count), pos);
    }

    nssv_constexpr size_type find_first_not_of(CharT const* s,
                                               size_type pos = 0) const  // (4)
    {
      return find_first_not_of(basic_string_view(s), pos);
    }

    // find_last_not_of(), 4x:

    nssv_constexpr size_type find_last_not_of(
        basic_string_view v, size_type pos = npos) const nssv_noexcept  // (1)
    {
      return empty() ? npos
                     : pos >= size()
                           ? find_last_not_of(v, size() - 1)
                           : to_pos(std::find_if(
                                 const_reverse_iterator(cbegin() + pos + 1),
                                 crend(), not_in_view(v)));
    }

    nssv_constexpr size_type
    find_last_not_of(CharT c, size_type pos = npos) const nssv_noexcept  // (2)
    {
      return find_last_not_of(basic_string_view(&c, 1), pos);
    }

    nssv_constexpr size_type find_last_not_of(CharT const* s, size_type pos,
                                              size_type count) const  // (3)
    {
      return find_last_not_of(basic_string_view(s, count), pos);
    }

    nssv_constexpr size_type
    find_last_not_of(CharT const* s, size_type pos = npos) const  // (4)
    {
      return find_last_not_of(basic_string_view(s), pos);
    }

    // Constants:

#if nssv_CPP17_OR_GREATER
    static nssv_constexpr size_type npos = size_type(-1);
#elif nssv_CPP11_OR_GREATER
    enum : size_type { npos = size_type(-1) };
#else
    enum { npos = size_type(-1) };
#endif

   private:
    struct not_in_view {
      const basic_string_view v;

      nssv_constexpr explicit not_in_view(basic_string_view v) : v(v) {}

      nssv_constexpr bool operator()(CharT c) const {
        return npos == v.find_first_of(c);
      }
    };

    nssv_constexpr size_type to_pos(const_iterator it) const {
      return it == cend() ? npos : size_type(it - cbegin());
    }

    nssv_constexpr size_type to_pos(const_reverse_iterator it) const {
      return it == crend() ? npos : size_type(crend() - it - 1);
    }

    nssv_constexpr const_reference data_at(size_type pos) const {
#if nssv_BETWEEN(nssv_COMPILER_GNUC_VERSION, 1, 500)
      return data_[pos];
#else
      return assert(pos < size()), data_[pos];
#endif
    }

   private:
    const_pointer data_;
    size_type size_;

   public:
#if nssv_CONFIG_CONVERSION_STD_STRING_CLASS_METHODS

    template <class Allocator>
    basic_string_view(std::basic_string<CharT, Traits, Allocator> const& s)
        nssv_noexcept : data_(s.data()),
                        size_(s.size()) {}

#if nssv_HAVE_EXPLICIT_CONVERSION

    template <class Allocator>
    explicit operator std::basic_string<CharT, Traits, Allocator>() const {
      return to_string(Allocator());
    }

#endif  // nssv_HAVE_EXPLICIT_CONVERSION

#if nssv_CPP11_OR_GREATER

    template <class Allocator = std::allocator<CharT> >
    std::basic_string<CharT, Traits, Allocator> to_string(
        Allocator const& a = Allocator()) const {
      return std::basic_string<CharT, Traits, Allocator>(begin(), end(), a);
    }

#else

    std::basic_string<CharT, Traits> to_string() const {
      return std::basic_string<CharT, Traits>(begin(), end());
    }

    template <class Allocator>
    std::basic_string<CharT, Traits, Allocator> to_string(
        Allocator const& a) const {
      return std::basic_string<CharT, Traits, Allocator>(begin(), end(), a);
    }

#endif  // nssv_CPP11_OR_GREATER

#endif  // nssv_CONFIG_CONVERSION_STD_STRING_CLASS_METHODS
  };

  //
  // Non-member functions:
  //

  // 24.4.3 Non-member comparison functions:
  // lexicographically compare two string views (function template):

  template <class CharT, class Traits>
  nssv_constexpr bool operator==(basic_string_view<CharT, Traits> lhs,
                                 basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) == 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator!=(basic_string_view<CharT, Traits> lhs,
                                 basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) != 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator<(basic_string_view<CharT, Traits> lhs,
                                basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) < 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator<=(basic_string_view<CharT, Traits> lhs,
                                 basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) <= 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator>(basic_string_view<CharT, Traits> lhs,
                                basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) > 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator>=(basic_string_view<CharT, Traits> lhs,
                                 basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) >= 0;
  }

  // Let S be basic_string_view<CharT, Traits>, and sv be an instance of S.
  // Implementations shall provide sufficient additional overloads marked
  // constexpr and noexcept so that an object t with an implicit conversion
  // to S can be compared according to Table 67.

#if !nssv_CPP11_OR_GREATER || nssv_BETWEEN(nssv_COMPILER_MSVC_VERSION, 100, 141)

  // accomodate for older compilers:

  // ==

  template <class CharT, class Traits>
  nssv_constexpr bool operator==(basic_string_view<CharT, Traits> lhs,
                                 char const* rhs) nssv_noexcept {
    return lhs.compare(rhs) == 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator==(
      char const* lhs, basic_string_view<CharT, Traits> rhs) nssv_noexcept {
    return rhs.compare(lhs) == 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator==(basic_string_view<CharT, Traits> lhs,
                                 std::basic_string<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.size() == rhs.size() && lhs.compare(rhs) == 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator==(std::basic_string<CharT, Traits> rhs,
                                 basic_string_view<CharT, Traits> lhs)
      nssv_noexcept {
    return lhs.size() == rhs.size() && lhs.compare(rhs) == 0;
  }

  // !=

  template <class CharT, class Traits>
  nssv_constexpr bool operator!=(basic_string_view<CharT, Traits> lhs,
                                 char const* rhs) nssv_noexcept {
    return lhs.compare(rhs) != 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator!=(
      char const* lhs, basic_string_view<CharT, Traits> rhs) nssv_noexcept {
    return rhs.compare(lhs) != 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator!=(basic_string_view<CharT, Traits> lhs,
                                 std::basic_string<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.size() != rhs.size() && lhs.compare(rhs) != 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator!=(std::basic_string<CharT, Traits> rhs,
                                 basic_string_view<CharT, Traits> lhs)
      nssv_noexcept {
    return lhs.size() != rhs.size() || rhs.compare(lhs) != 0;
  }

  // <

  template <class CharT, class Traits>
  nssv_constexpr bool operator<(basic_string_view<CharT, Traits> lhs,
                                char const* rhs) nssv_noexcept {
    return lhs.compare(rhs) < 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator<(
      char const* lhs, basic_string_view<CharT, Traits> rhs) nssv_noexcept {
    return rhs.compare(lhs) > 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator<(basic_string_view<CharT, Traits> lhs,
                                std::basic_string<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) < 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator<(std::basic_string<CharT, Traits> rhs,
                                basic_string_view<CharT, Traits> lhs)
      nssv_noexcept {
    return rhs.compare(lhs) > 0;
  }

  // <=

  template <class CharT, class Traits>
  nssv_constexpr bool operator<=(basic_string_view<CharT, Traits> lhs,
                                 char const* rhs) nssv_noexcept {
    return lhs.compare(rhs) <= 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator<=(
      char const* lhs, basic_string_view<CharT, Traits> rhs) nssv_noexcept {
    return rhs.compare(lhs) >= 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator<=(basic_string_view<CharT, Traits> lhs,
                                 std::basic_string<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) <= 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator<=(std::basic_string<CharT, Traits> rhs,
                                 basic_string_view<CharT, Traits> lhs)
      nssv_noexcept {
    return rhs.compare(lhs) >= 0;
  }

  // >

  template <class CharT, class Traits>
  nssv_constexpr bool operator>(basic_string_view<CharT, Traits> lhs,
                                char const* rhs) nssv_noexcept {
    return lhs.compare(rhs) > 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator>(
      char const* lhs, basic_string_view<CharT, Traits> rhs) nssv_noexcept {
    return rhs.compare(lhs) < 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator>(basic_string_view<CharT, Traits> lhs,
                                std::basic_string<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) > 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator>(std::basic_string<CharT, Traits> rhs,
                                basic_string_view<CharT, Traits> lhs)
      nssv_noexcept {
    return rhs.compare(lhs) < 0;
  }

  // >=

  template <class CharT, class Traits>
  nssv_constexpr bool operator>=(basic_string_view<CharT, Traits> lhs,
                                 char const* rhs) nssv_noexcept {
    return lhs.compare(rhs) >= 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator>=(
      char const* lhs, basic_string_view<CharT, Traits> rhs) nssv_noexcept {
    return rhs.compare(lhs) <= 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator>=(basic_string_view<CharT, Traits> lhs,
                                 std::basic_string<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) >= 0;
  }

  template <class CharT, class Traits>
  nssv_constexpr bool operator>=(std::basic_string<CharT, Traits> rhs,
                                 basic_string_view<CharT, Traits> lhs)
      nssv_noexcept {
    return rhs.compare(lhs) <= 0;
  }

#else  // newer compilers:

#define nssv_BASIC_STRING_VIEW_I(T, U) \
  typename std::decay<basic_string_view<T, U> >::type

#if nssv_BETWEEN(nssv_COMPILER_MSVC_VERSION, 140, 150)
#define nssv_MSVC_ORDER(x) , int = x
#else
#define nssv_MSVC_ORDER(x) /*, int=x*/
#endif

  // ==

  template <class CharT, class Traits nssv_MSVC_ORDER(1)>
  nssv_constexpr bool operator==(basic_string_view<CharT, Traits> lhs,
                                 nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                     rhs) nssv_noexcept {
    return lhs.compare(rhs) == 0;
  }

  template <class CharT, class Traits nssv_MSVC_ORDER(2)>
  nssv_constexpr bool operator==(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
                                 basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.size() == rhs.size() && lhs.compare(rhs) == 0;
  }

  // !=

  template <class CharT, class Traits nssv_MSVC_ORDER(1)>
  nssv_constexpr bool operator!=(basic_string_view<CharT, Traits> lhs,
                                 nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                     rhs) nssv_noexcept {
    return lhs.size() != rhs.size() || lhs.compare(rhs) != 0;
  }

  template <class CharT, class Traits nssv_MSVC_ORDER(2)>
  nssv_constexpr bool operator!=(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
                                 basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) != 0;
  }

  // <

  template <class CharT, class Traits nssv_MSVC_ORDER(1)>
  nssv_constexpr bool operator<(basic_string_view<CharT, Traits> lhs,
                                nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                    rhs) nssv_noexcept {
    return lhs.compare(rhs) < 0;
  }

  template <class CharT, class Traits nssv_MSVC_ORDER(2)>
  nssv_constexpr bool operator<(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
                                basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) < 0;
  }

  // <=

  template <class CharT, class Traits nssv_MSVC_ORDER(1)>
  nssv_constexpr bool operator<=(basic_string_view<CharT, Traits> lhs,
                                 nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                     rhs) nssv_noexcept {
    return lhs.compare(rhs) <= 0;
  }

  template <class CharT, class Traits nssv_MSVC_ORDER(2)>
  nssv_constexpr bool operator<=(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
                                 basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) <= 0;
  }

  // >

  template <class CharT, class Traits nssv_MSVC_ORDER(1)>
  nssv_constexpr bool operator>(basic_string_view<CharT, Traits> lhs,
                                nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                    rhs) nssv_noexcept {
    return lhs.compare(rhs) > 0;
  }

  template <class CharT, class Traits nssv_MSVC_ORDER(2)>
  nssv_constexpr bool operator>(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
                                basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) > 0;
  }

  // >=

  template <class CharT, class Traits nssv_MSVC_ORDER(1)>
  nssv_constexpr bool operator>=(basic_string_view<CharT, Traits> lhs,
                                 nssv_BASIC_STRING_VIEW_I(CharT, Traits)
                                     rhs) nssv_noexcept {
    return lhs.compare(rhs) >= 0;
  }

  template <class CharT, class Traits nssv_MSVC_ORDER(2)>
  nssv_constexpr bool operator>=(nssv_BASIC_STRING_VIEW_I(CharT, Traits) lhs,
                                 basic_string_view<CharT, Traits> rhs)
      nssv_noexcept {
    return lhs.compare(rhs) >= 0;
  }

#undef nssv_MSVC_ORDER
#undef nssv_BASIC_STRING_VIEW_I

#endif  // compiler-dependent approach to comparisons

  // 24.4.4 Inserters and extractors:

  namespace detail {

  template <class Stream>
  void write_padding(Stream& os, std::streamsize n) {
    for (std::streamsize i = 0; i < n; ++i) os.rdbuf()->sputc(os.fill());
  }

  template <class Stream, class View>
  Stream& write_to_stream(Stream& os, View const& sv) {
    typename Stream::sentry sentry(os);

    if (!os) return os;

    const std::streamsize length = static_cast<std::streamsize>(sv.length());

    // Whether, and how, to pad:
    const bool pad = (length < os.width());
    const bool left_pad = pad && (os.flags() & std::ios_base::adjustfield) ==
                                     std::ios_base::right;

    if (left_pad) write_padding(os, os.width() - length);

    // Write span characters:
    os.rdbuf()->sputn(sv.begin(), length);

    if (pad && !left_pad) write_padding(os, os.width() - length);

    // Reset output stream width:
    os.width(0);

    return os;
  }

  }  // namespace detail

  template <class CharT, class Traits>
  std::basic_ostream<CharT, Traits>& operator<<(
      std::basic_ostream<CharT, Traits>& os,
      basic_string_view<CharT, Traits> sv) {
    return detail::write_to_stream(os, sv);
  }

  // Several typedefs for common character types are provided:

  typedef basic_string_view<char> string_view;
  typedef basic_string_view<wchar_t> wstring_view;
#if nssv_HAVE_WCHAR16_T
  typedef basic_string_view<char16_t> u16string_view;
  typedef basic_string_view<char32_t> u32string_view;
#endif

  }  // namespace sv_lite
}  // namespace nonstd::sv_lite

//
// 24.4.6 Suffix for basic_string_view literals:
//

#if nssv_HAVE_USER_DEFINED_LITERALS

namespace nonstd {
nssv_inline_ns namespace literals {
  nssv_inline_ns namespace string_view_literals {

#if nssv_CONFIG_STD_SV_OPERATOR && nssv_HAVE_STD_DEFINED_LITERALS

    nssv_constexpr nonstd::sv_lite::string_view operator"" sv(
        const char* str, size_t len) nssv_noexcept  // (1)
    {
      return nonstd::sv_lite::string_view{str, len};
    }

    nssv_constexpr nonstd::sv_lite::u16string_view operator"" sv(
        const char16_t* str, size_t len) nssv_noexcept  // (2)
    {
      return nonstd::sv_lite::u16string_view{str, len};
    }

    nssv_constexpr nonstd::sv_lite::u32string_view operator"" sv(
        const char32_t* str, size_t len) nssv_noexcept  // (3)
    {
      return nonstd::sv_lite::u32string_view{str, len};
    }

    nssv_constexpr nonstd::sv_lite::wstring_view operator"" sv(
        const wchar_t* str, size_t len) nssv_noexcept  // (4)
    {
      return nonstd::sv_lite::wstring_view{str, len};
    }

#endif  // nssv_CONFIG_STD_SV_OPERATOR && nssv_HAVE_STD_DEFINED_LITERALS

#if nssv_CONFIG_USR_SV_OPERATOR

    nssv_constexpr nonstd::sv_lite::string_view operator"" _sv(
        const char* str, size_t len) nssv_noexcept  // (1)
    {
      return nonstd::sv_lite::string_view{str, len};
    }

    nssv_constexpr nonstd::sv_lite::u16string_view operator"" _sv(
        const char16_t* str, size_t len) nssv_noexcept  // (2)
    {
      return nonstd::sv_lite::u16string_view{str, len};
    }

    nssv_constexpr nonstd::sv_lite::u32string_view operator"" _sv(
        const char32_t* str, size_t len) nssv_noexcept  // (3)
    {
      return nonstd::sv_lite::u32string_view{str, len};
    }

    nssv_constexpr nonstd::sv_lite::wstring_view operator"" _sv(
        const wchar_t* str, size_t len) nssv_noexcept  // (4)
    {
      return nonstd::sv_lite::wstring_view{str, len};
    }

#endif  // nssv_CONFIG_USR_SV_OPERATOR
  }
}
}  // namespace nonstd

#endif

//
// Extensions for std::string:
//

#if nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS

namespace nonstd {
namespace sv_lite {

// Exclude MSVC 14 (19.00): it yields ambiguous to_string():

#if nssv_CPP11_OR_GREATER && nssv_COMPILER_MSVC_VERSION != 140

template <class CharT, class Traits, class Allocator = std::allocator<CharT> >
std::basic_string<CharT, Traits, Allocator> to_string(
    basic_string_view<CharT, Traits> v, Allocator const& a = Allocator()) {
  return std::basic_string<CharT, Traits, Allocator>(v.begin(), v.end(), a);
}

#else

template <class CharT, class Traits>
std::basic_string<CharT, Traits> to_string(basic_string_view<CharT, Traits> v) {
  return std::basic_string<CharT, Traits>(v.begin(), v.end());
}

template <class CharT, class Traits, class Allocator>
std::basic_string<CharT, Traits, Allocator> to_string(
    basic_string_view<CharT, Traits> v, Allocator const& a) {
  return std::basic_string<CharT, Traits, Allocator>(v.begin(), v.end(), a);
}

#endif  // nssv_CPP11_OR_GREATER

template <class CharT, class Traits, class Allocator>
basic_string_view<CharT, Traits> to_string_view(
    std::basic_string<CharT, Traits, Allocator> const& s) {
  return basic_string_view<CharT, Traits>(s.data(), s.size());
}

}  // namespace sv_lite
}  // namespace nonstd

#endif  // nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS

//
// make types and algorithms available in namespace nonstd:
//

namespace nonstd {

using sv_lite::basic_string_view;
using sv_lite::string_view;
using sv_lite::wstring_view;

#if nssv_HAVE_WCHAR16_T
using sv_lite::u16string_view;
#endif
#if nssv_HAVE_WCHAR32_T
using sv_lite::u32string_view;
#endif

// literal "sv"

using sv_lite::operator==;
using sv_lite::operator!=;
using sv_lite::operator<;
using sv_lite::operator<=;
using sv_lite::operator>;
using sv_lite::operator>=;

using sv_lite::operator<<;

#if nssv_CONFIG_CONVERSION_STD_STRING_FREE_FUNCTIONS
using sv_lite::to_string;
using sv_lite::to_string_view;
#endif

}  // namespace nonstd

// 24.4.5 Hash support (C++11):

// Note: The hash value of a string view object is equal to the hash value of
// the corresponding string object.

#if nssv_HAVE_STD_HASH

#include <functional>

namespace std {

template <>
struct hash<nonstd::string_view> {
 public:
  std::size_t operator()(nonstd::string_view v) const nssv_noexcept {
    return std::hash<std::string>()(std::string(v.data(), v.size()));
  }
};

template <>
struct hash<nonstd::wstring_view> {
 public:
  std::size_t operator()(nonstd::wstring_view v) const nssv_noexcept {
    return std::hash<std::wstring>()(std::wstring(v.data(), v.size()));
  }
};

template <>
struct hash<nonstd::u16string_view> {
 public:
  std::size_t operator()(nonstd::u16string_view v) const nssv_noexcept {
    return std::hash<std::u16string>()(std::u16string(v.data(), v.size()));
  }
};

template <>
struct hash<nonstd::u32string_view> {
 public:
  std::size_t operator()(nonstd::u32string_view v) const nssv_noexcept {
    return std::hash<std::u32string>()(std::u32string(v.data(), v.size()));
  }
};

}  // namespace std

#endif  // nssv_HAVE_STD_HASH

nssv_RESTORE_WARNINGS()

#endif  // nssv_HAVE_STD_STRING_VIEW
#endif  // NONSTD_SV_LITE_H_INCLUDED